Method for connecting a plurality of computer terminals to a broadband cable

ABSTRACT

A plurality of computer terminals ( 18 ), intended to be placed at different places within a restricted local area, are connected to an external broadband cable ( 19 ), intended for bidirectional transmission of data in the form of base band signals, by utilizing an existing local coaxial cable TV network ( 10 ) to which the computer terminals ( 18 ) and the broadband cable ( 19 ) are connected through the intermediary of modulator and demodulator means ( 22, 24 ) which are arranged to permit data to be transmitted on said network ( 10 ) in both directions between the computer terminals ( 18 ) and the broadband cable ( 19 ) in the form of modulated carrier signals having carrier frequencies lying outside the frequency bands utilized for the distribution of TV and/or radio signals on said network ( 10 ).

The present invention relates to a method for connecting a plurality ofcomputer terminals, intended to be placed at different places within arestricted local area, to an external broadband cable, intended forbidirectional transmission of data in the form of base band signals.

In order to facilitate a transmission of data at a high speed betweendifferent computer users and a communication central, common to a largenumber of such users, it has become more and more frequent in recentyears, from a communication central and to different local areas, to runbroadband cables on which data can be transmitted in the form of opticalor electric base band signals. However, in many cases, the connection ofdifferent computer users, residing within a certain local area, to theexternal broadband cable run to said area has been strongly delayed dueto the fact that, hitherto, said connection has consistently beeneffected by running a separate connection line from said cable to eachindividual computer user, i.e. by a method that in practice implies atroublesome and time-consuming and hence costly installation.

The invention has for its purpose to provide an improved method of thekind initially specified which makes it possible to effect the desiredconnection between each separate computer terminal within the local areain question and the external broadband cable in a substantiallysimplified, more rapid and less costly manner.

The method according to the invention proposed for said purpose isprimarily characterized by connecting the computer terminals to thebroadband cable via an existing local coaxial cable network, serving todistribute TV and/or radio signals to different places within the localarea in question, the computer terminals and the broadband cable beingconnected to said network through the intermediary of modulator anddemodulator means which are arranged to permit data to be transmitted onsaid network in both directions between the computer terminals and thebroadband cable in the form of modulated carrier signals having carrierfrequencies within frequency bands lying outside the frequency bandsused for the distribution of TV and/or radio signals.

The invention fully eliminates the previous need for installing specialconnection lines between the external broadband cable and the computerterminals.

In order to simplify the installation of the required supplementaryequipment at each separate computer user location, the computerterminals may preferably be connected to the coaxial cable network viaexisting TV signal outlets of said network. This means that, if thecoaxial cable network for instance is installed in an apartment block,the connection of the computer terminals to the coaxial cable networkcan be effected by the apartment owners themselves and thus, it is notrequired to engage an installer for said purpose.

The computer terminals may in this case suitably be connected to theexisting TV signal outlets by means of respective connection units, eachof which comprises means for separating TV signals transmitted on thenetwork from data signals transmitted thereon and diverting the TVsignals to a supplementary TV signal outlet and preferably alsocontaining the modulator and demodulator means of the computer terminalin question.

In order to make a very broad carrier frequency band disposable for thedata transmission between the broadband cable and the computerterminals, said cable and the computer terminals may be connected to thecoaxial cable network through the intermediary of modulator anddemodulator means which-are arranged to permit the data transmission onsaid network in both directions to be effected while utilizing carrierfrequencies within frequency bands lying above the carrier frequencybands intended for the distribution of TV and/or radio signals. Asuitable interval for the data transmission on the coaxial cable networkis from about 900 MHz to about 2000 MHz.

In order to prevent unauthorized people from picking up the data signalstransmitted to or from a certain computer terminal, the modulator anddemodulator means used for connecting the broadband cable and thecomputer terminals to the coaxial cable network may, when so required,be arranged to permit the data transmission on said network to beeffected while utilizing mutually different carrier frequencies fordifferent computer terminals.

In order to facilitate a simultaneous data transmission to and from acomputer terminal, i.e. full duplex, it is possible, for the connectionof the broadband cable and the computer terminals to the coaxial cablenetwork, to use modulator and demodulator means which are arranged toutilize mutually different carrier frequencies for the data transmissionin mutually opposite directions on said network.

Below the invention is further described with reference to theaccompanying drawings, in which

FIG. 1 shows a block diagram of a local installation, selected by way ofexample only, where the method according to the invention has been usedfor connecting a plurality of computer terminals to an externalbroadband cable,

FIG. 2 shows a block diagram of a combined modulator and demodulatorunit according to a first kind of such units contained in saidinstallation, and

FIG. 3 shows a block diagram of a combined modulator and demodulatorunit according to a second kind of such units contained in saidinstallation.

In FIG. 1, reference numeral 10 generally designates a local coaxialcable TV network of tree and branch type comprising an input 11,intended to be connected to an external coaxial cable 12, on which, froman external source not shown, network 10 may be supplied with TV andradio signals consisting of modulated carrier signals having carrierfrequencies lying within a predetermined frequency band, e.g. 47 to 860MHz.

From input 11, said signals are distributed via a main line 13 ofnetwork 10 and a plurality of branch lines 14, connected to said mainline, to a plurality of outlet boxes 15, connected each to one of saidbranch lines and provided at different subscribers and each of whichcomprises a radio signal outlet 16 and a TV signal outlet 17.

Apart from being used for the distribution of TV and radio signals,network 10 may also be used for bidirectional transmission of data inthe form of modulated carrier signals between a plurality of computerterminals 18, provided at different subscribers, and an externalbroadband cable 19 on which said data can be transmitted in the form ofbase band signals to or from a communication central, not shown, whichmay be located at a large distance from the local area covered bynetwork 10.

For this purpose, the installation comprises a coupling unit 21,connected to cable 19 via a combined input and output 20, and aplurality of combined modulator lator and demodulator units 22,connected to said coupling unit and forming a separate unit of said kindfor each individual computer terminal 18. Units 22, the more detailedstructure of which appears from FIG. 2, are all connected to network 10via a diplex filter 23, connected in main line 13 and having for itspurpose to prevent data signals transmitted on network 10 from being fedout on cable 12 and via said cable to other local networks and toprevent any disturbances appearing on cable 12 and having frequencieslying outside the frequency band utilized for the transmission of TV andradio signals from being transmitted to network 10.

Furthermore, the installation also comprises a corresponding pluralityof combined modulator and demodulator units 24 which are connected eachto the TV signal outlet 17 of one outlet box 15 via a connection unit 25which is provided with a supplementary TV signal outlet 26 to which itis arranged to divert incoming TV signals. Unit 25, which in practicemay be united with unit 24 and also computer terminal 18, may preferablycomprise a diplex filter. The more detailed structure of units 24appears from FIG. 3.

Units 22 have for their purpose to convert data, incoming in the form ofbase band signals from cable 19 via unit 21, to corresponding modulatedcarrier signals and to deliver the latter signals to line 13. In acorresponding manner, units 24 have for their purpose to convert data,incoming in the form of base band signals via computer terminals 18, tocorresponding modulated carrier signals and to deliver the lattersignals to network 10. Moreover, units 22 also serve to convertmodulated carrier signals, transmitted to them from units 24 via network10, to corresponding base band signals and to deliver the latter signalsto unit 21 for subsequently outputting them on cable 19, while units 24serve to convert modulated carrier signals, transmitted to them fromunits 22, to corresponding base band signals and to deliver the lattersignals to the respective computer terminals 18.

As may be seen from FIG. 2, each unit 22 comprises an input 27,connected to unit 21 (FIG. 1), and an output 28, also connected to unit21. Additionally, it also comprises two sine wave generators 31 and 32,connected each to one mixer 29 and 30, respectively, and a diplex filter34, connected to a combined input and output 33 which in its turn isconnected to diplex filter 23 (FIG. 1).

In a corresponding manner, each unit 24 comprises an output 18′ and aninput 18″ which together form a computer terminal 18 (FIG. 1) to which acomputer may be connected. Furthermore, each unit 24 also comprises twosine wave generators 37 and 38 which are connected each to one mixer 35and 36, respectively, and a diplex filter 40, connected to a combinedinput and output 39 which in its turn is connected to connection unit 25(FIG. 1).

In order to make sure that each separate unit 22 will cooperate in theabove described manner only with the particular unit 24, intended tocooperate therewith, sine wave generators 31 and 37 of said twocooperating units are arranged to generate a sine wave having apredetermined unique frequency f′, while sine wave generators 32 and 38of said two units are arranged to generate a sine wave having anotherpredetermined unique frequency f″.

Hereby, mixer 29 will transform the data received via input 27 andconsisting of base band signals to corresponding modulated carriersignals having the carrier frequency f′. When reaching mixer 35, thelatter signals will then be demodulated by said mixer and becomereconverted into base band signals that may be fed out via output 18′.

In corresponding manner, by means of mixer 36, base band signalsincoming via input 18″ will be converted into corresponding modulatedcarrier signals having the carrier frequency f″ which then by means ofmixer 30 are reconverted into base band signals that can be fed out viaoutput 28.

For all pairs of cooperating units 22 and 24, said carrier frequenciesmay suitably be selected within a frequency band lying above thefrequency bands utilized for the distribution of radio and TV signals.Thus, one may for instance use carrier frequencies within the intervalfrom about 900 MHz to about 2000 MHz for the transmission of data.

The invention is not restricted to the embodiment above described andshown in the drawings. Instead, many other embodiments are feasiblewithin the scope of the invention as defined in the following claims. Byway of example, it could be mentioned that the invention may be appliedalso in connection with other types of local coaxial cable networks thantree and branch networks. For instance, the local network may consist ofa star network. Finally, it should be mentioned that the expression“computer terminal” herein used is intended to include any kind ofterminal or other connection means to which a computer may be directlyor indirectly connected.

1-7. (canceled)
 8. A method for connecting a plurality of computerterminals placed at different places within a restricted local area, toan external broadband cable for bidirectional transmission of data inthe form of base band signals, said method comprising connecting thecomputer terminals to the broadband cable via an existing local coaxialcable network which forms a restricted local portion of a cable TVsystem and serves to distribute broadcast signals to different placeswithin said area from an external broadcast signal source connected tosaid network by another external cable, wherein the computer terminalsand the broadband cable are connected to said network through modulatorand demodulator means which are arranged to permit data to betransmitted on said network in both directions between the computerterminals and the broadband cable in the form of modulated carriersignals having carrier frequencies within frequency bands lying abovecarrier frequency bands used for distributing the broadcast signals. 9.A method according to claim 8, wherein the computer terminals areconnected to the local coaxial cable network via existing TV signaloutlets of said network.
 10. A method according to claim 9, wherein thecomputer terminals are connected to the existing TV signal outlets byrespective connection units, each connection unit comprising means forseparating TV signals transmitted on the local coaxial cable networkfrom data signals transmitted on said network and diverting the TVsignals to a supplementary TV signal outlet.
 11. A method according toclaim 10, wherein said connection units also contain the modulator anddemodulator means for the respective computer terminals.
 12. A methodaccording to claim 1, wherein the modulator and demodulator means arearranged to permit the data transmission on the local coaxial cablenetwork to be effected utilizing carrier frequencies in the range fromabout 900 MHz to about 2000 MHz.
 13. A method according to claim 1,wherein the broadband cable and the computer terminals are connected tothe local coaxial cable network through modulator and demodulator meansarranged to permit the data transmission on said network to be effectedutilizing mutually different carrier frequencies for different computerterminals.
 14. A method according to claim 1, wherein the broadbandcable and the computer terminals are connected to the local coaxialcable network through modulator and demodulator means arranged to permitmutually different carrier frequencies to be utilized for the datatransmission in mutually opposite directions on said network.